16 THE VOYAGE OF H.M.S. CHALLENGER. 



were for the most part found on the surface of the reef, have a greenish tinge, as if they 

 lived on the corresponding particles of the Chlorosperm AlgcB. When growing attached 

 to marine plants, the animal bodies of Orhitolites may be nourished by the gelatinous 

 investment with which those plants are covered. In my former Memoir I mentioned 

 that some of the spirit-specimens I had then examined by decalcification proved to be 

 invested by a sort of cuticle formed of Diatoms, Desmids, and other minute Algce ; but 

 I have not met with any such investment among the large number of spirit-specimens 

 of both types which I have examined in the Challenger collection. 



As to the Reproduction of Orhitolites, I regret to be unable to afford the least 

 information, having searched in vain for any further evidence of the mode in which it is 

 effected, than that which I had formerly obtained. In my Introduction to the Study of 

 the Foraminifera (p. 38) I described and figured some extremely young specimens of 

 Orhitolites, consisting only of the " nucleus " and a single annulus of sub-segments, — 

 which had been taken out from the grooved margin of a large plicated disk, resembling 

 those figured in PI. VII. And I have found similar specimens in the same situation in 

 some of the large Fijian disks.^ As I shall hereafter state more in detail, the marginal 

 annuli of the largest disks often have no radial partitions, their cavities being continuously 

 annular ; and as the thin external walls of these annuli, being unsupported by internal 

 partitions, are very fragile, it may not be thought unlikely that gemmules may be formed 

 within these peripheral zones, which may be set free by the rupture of this wall, and may 

 retain for a time the protection of the overhanging superficial lamellae, which form a deep 

 channel for their lodgment. Of a very curious variation in the mode of growth of 

 Orhitolites complanata, which seems constantly related to the size of the " nucleus " in 

 which it commences, particulars -ftoU be given hereafter (pp. 38, 41). 



1. Orhitolites tenuissima, Carpenter (Pis. I. and II.). 



Orbitolites tenuisdmus, Carpenter and Jeffreys, Proc. Eoy. Soc, voL xviii., 1869, p. 421, and 

 vol. xix., 1870, p. 155. 



This very beautiful and most interesting form of the Orbitoline t)^e (Pis. I. and II.) 

 was first obtained in the deep-sea dredgings of the "Porcupine" expedition of 1869, 

 between the north-west of Ireland and the Eockall Bank ; and has been subsequently 

 brought up from abyssal depths in other parts of the North Atlantic, as also from shore 

 bottoms off the coast of Portugal, and within the Mediterranean. It is at once distin- 

 guished from all other specific forms by the extreme disproportion between the area and 

 the thickness of its disks ; for whilst its largest examples approach in diameter the smaller 

 specimens of Orhitolites complanata, and their surface presents the same regular 



' Such 3'oung disks will be found represented in PI. XVI. figs. 1-4, of Mr. Brady's Report on the Foraminifera of 

 the Challenger Expedition, Zool. ChaU. Exp., part xxii. 



I 



